Painted Hills unit of John Day National Monument.
On one of my summer vacation bike trips around in the Pacific Northwest, I visited the Painted Hills near Prineville in central Oregon.  Oregon's heartland is a geological paradise.  Mostly dry, as it lies on the east side of the Cascade Mountains, the region is full of old falt lines, lava formations and other features that are preserved and exposed by the dry climate.  These mud hills are among the many unusual things to see.

My larger images on Flickr.

John Day Painted Hills